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<h1>The simpleViewer example</h1>

<center>
  <img src="../images/simpleViewer.jpg" width="330" height="228" alt="simpleViewer"/>
</center>

<p>
 The simplest application example: 20 lines of code and yet all the power !
</p>
<p>
 A Viewer class is derived from QGLViewer and its <code>draw()</code> function is overloaded to
 specify the user defined OpenGL orders that describe the scene.
</p>
<p>
 This is the first example you should try, as it explains some of the default keyboard shortcuts
 and the mouse behavior of the viewer.
</p>
<p>
 This example can be cut and pasted to start the development of a new application.
</p>
<h2>simpleViewer.h</h2>
<pre>
#include &lt;QGLViewer/qglviewer.h&gt;

class Viewer : public QGLViewer {
protected:
  virtual void draw();
  virtual void init();
  virtual QString helpString() const;
};
</pre>


<h2>simpleViewer.cpp</h2>
<pre>
#include "simpleViewer.h"

using namespace std;

// Draws a spiral
void Viewer::draw() {
  const float nbSteps = 200.0;

  glBegin(GL_QUAD_STRIP);
  for (int i = 0; i &lt; nbSteps; ++i) {
    const float ratio = i / nbSteps;
    const float angle = 21.0 * ratio;
    const float c = cos(angle);
    const float s = sin(angle);
    const float r1 = 1.0 - 0.8f * ratio;
    const float r2 = 0.8f - 0.8f * ratio;
    const float alt = ratio - 0.5f;
    const float nor = 0.5f;
    const float up = sqrt(1.0 - nor * nor);
    glColor3f(1.0 - ratio, 0.2f, ratio);
    glNormal3f(nor * c, up, nor * s);
    glVertex3f(r1 * c, alt, r1 * s);
    glVertex3f(r2 * c, alt + 0.05f, r2 * s);
  }
  glEnd();
}

void Viewer::init() {
  // Restore previous viewer state.
  restoreStateFromFile();

  // Opens help window
  help();
}

QString Viewer::helpString() const {
  QString text("&lt;h2&gt;S i m p l e V i e w e r&lt;/h2&gt;");
  text += "Use the mouse to move the camera around the object. ";
  text += "You can respectively revolve around, zoom and translate with the "
          "three mouse buttons. ";
  text += "Left and middle buttons pressed together rotate around the camera "
          "view direction axis&lt;br&gt;&lt;br&gt;";
  text += "Pressing &lt;b&gt;Alt&lt;/b&gt; and one of the function keys "
          "(&lt;b&gt;F1&lt;/b&gt;..&lt;b&gt;F12&lt;/b&gt;) defines a camera keyFrame. ";
  text += "Simply press the function key again to restore it. Several "
          "keyFrames define a ";
  text += "camera path. Paths are saved when you quit the application and "
          "restored at next start.&lt;br&gt;&lt;br&gt;";
  text +=
      "Press &lt;b&gt;F&lt;/b&gt; to display the frame rate, &lt;b&gt;A&lt;/b&gt; for the world axis, ";
  text += "&lt;b&gt;Alt+Return&lt;/b&gt; for full screen mode and &lt;b&gt;Control+S&lt;/b&gt; to save "
          "a snapshot. ";
  text += "See the &lt;b&gt;Keyboard&lt;/b&gt; tab in this window for a complete shortcut "
          "list.&lt;br&gt;&lt;br&gt;";
  text += "Double clicks automates single click actions: A left button double "
          "click aligns the closer axis with the camera (if close enough). ";
  text += "A middle button double click fits the zoom of the camera and the "
          "right button re-centers the scene.&lt;br&gt;&lt;br&gt;";
  text += "A left button double click while holding right button pressed "
          "defines the camera &lt;i&gt;Revolve Around Point&lt;/i&gt;. ";
  text += "See the &lt;b&gt;Mouse&lt;/b&gt; tab and the documentation web pages for "
          "details.&lt;br&gt;&lt;br&gt;";
  text += "Press &lt;b&gt;Escape&lt;/b&gt; to exit the viewer.";
  return text;
}
</pre>


<h2>main.cpp</h2>
<pre>
#include "simpleViewer.h"
#include &lt;qapplication.h&gt;

int main(int argc, char **argv) {
  // Read command lines arguments.
  QApplication application(argc, argv);

  // Instantiate the viewer.
  Viewer viewer;

  viewer.setWindowTitle("simpleViewer");

  // Make the viewer window visible on screen.
  viewer.show();

  // Run main loop.
  return application.exec();
}
</pre>



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